There is a communication mode for transferring data transferred from a base station side to a data terminal device such as a personal computer (PC) or the like using a communication terminal such as a cellular phone as a communication modem or router.
An optimal communication path can be built according to an Internet Protocol (IP) address, by a communication terminal having a router function being connected to a personal digital assistant (PDA) or PC (e.g., Japanese Laid-open Patent Publication No. 2005-217994).
The 3rd Generation Partnership Project (3GPP) stipulates Long Term Evolution (LTE) for 3.9G. With the communication standard of LTE, compression or decompression of an IP packet header can be performed at the layer 2 that is Packet Data Convergence Protocol (PDCP). That is to say, transmission or reception of a compressed header can be performed between a communication terminal and an LTE base station.